Hydrocarbons recovery

ABSTRACT

Methods and systems of separating a hydrocarbon phase from a mixture comprising an emulsion of water and hydrocarbons in the presence of a surfactant, comprising adjusting the salinity of the mixture to release hydrocarbons and water from the emulsion into a hydrocarbon phase and a salt-containing aqueous phase respectively; and separating at least a part of the hydrocarbon phase from the salt-containing aqueous phase wherein at least a part of the salt-containing aqueous phase is recovered for further use.

FIELD OF THE INVENTION

This invention relates to the recovery of hydrocarbons. In particular,though not exclusively, the invention relates to improved processes andapparatus for separating mixtures comprising an emulsion of hydrocarbonsand water.

BACKGROUND OF THE INVENTION

Hydrocarbons are a large class of organic compounds composed of hydrogenand carbon. For example, crude oils, natural gas, kerogen, bitumen,pyrobitumen and asphaltenes are all mixtures of various hydrocarbons.Though hydrocarbons are generally defined as molecules formed primarilyof carbon and hydrogen atoms, they may also include other elements, suchas, but not limited to, halogens, metallic elements, nitrogen, oxygenand/or sulfur.

Hydrocarbons are typically recovered or produced from subterraneanformations by a variety of methods. “Primary recovery” techniques referto those techniques that utilise energy from the formation itself torecover the hydrocarbons in the subterranean formation. However primaryrecovery techniques are only capable of producing a small fraction ofthe oil in place in the reservoir. Consequently secondary techniques,such as waterflooding, and numerous tertiary techniques (commonlyreferred to as “enhanced oil recovery” (EOR) techniques), have beendeveloped, which have as their primary purpose the recovery ofadditional quantities of hydrocarbons known to be present in thereservoir.

One of the most common secondary techniques is waterflooding. However,even after a typical waterflood the reservoir may retain a great portionof its hydrocarbons in place. It is well known that much of the retainedhydrocarbons in the reservoir after a typical waterflood are in the formof globules or droplets that are trapped in the pore spaces of thereservoir. The high normal interfacial tension between the reservoirwater and hydrocarbons prevents these discrete droplets from deformingto pass through narrow constrictions in pore channels.

In certain tertiary techniques, referred to as “chemical enhanced oilrecovery” (cEOR) techniques, surface-active agents or surfactants havebeen added to flood water solutions to lower the interfacial tensionbetween the water and hydrocarbons and thereby allow hydrocarbondroplets to deform and flow with injected floodwater. It is generallythought that the interfacial tension between the oil and water must bereduced from the normal reservoir interfacial tension, that is on theorder of about 20 dyne/cm, to less than 0.1 dyne/cm for effectiverecovery.

Many patents describe cEOR utilizing chemical surfactants and polymers,including among others U.S. Pat. Nos. 3,508,611, 3,823,777, 3,981,361,4,058,467, 4,203,491, 4,232,738, 4,362,212, 4,411,816, 4,458,755,4,493,371, 4,501,675, 4,502,541, 4,799,547, 5,031,698, 5,068,043,6,022,834, 6,613,720, 6,989,355 and Canadian Pat. No. 1,169,759.Fundamentally, as indicated in SPE Paper No. 7053 presented at asymposium on improved methods for oil recovery in April 1978, twoessential criteria must generally be met for successful recovery ofresidual oil by chemical flooding: (1) very low interfacial tensionbetween the chemical bank and the residual oil and between the chemicalbank and the drive fluid, and (2) small surfactant retention losses tothe reservoir rock.

During cEOR, low interfacial tension in the chemical bank typicallyresults in the formation of microemulsions (see for example U.S. Pat.No. 3,254,714, Gogarty et al, issued June 1966, and U.S. Pat. No.3,981,361 Healy, issued Sep. 21, 1976). Microemulsions, which may beinjected or formed within a hydrocarbons formation, are miscellarmixtures of oil, water and a surfactant, frequently in combination witha co-surfactant, co-solvent or other chemicals. There is some scientificdebate as to the exact structure of microemulsions; in thisspecification, the term “microemulsion” refers broadly to emulsionswhich are thermodynamically stable.

Formulation of injection mixtures in enhanced hydrocarbons recovery isoften based on the identification of state variables that lead to aso-called “middle-phase” (or Winsor type-III) microemulsion inequilibrium with both excess hydrocarbons and excess water. “Optimalsalinity” is usually thought of as the specific salt concentration thatproduces the lowest interfacial tension between oil and water in a givenmixture and thus results in a middle phase microemulsion.

In those reservoirs that have been subjected to a cEOR flood, therecovered liquid from a producing well is usually in the form of amixture (emulsion) comprising hydrocarbons, water and a surfactant.These mixtures are relatively stable because of reduced interfacialtension and typically comprise, as one component, a microemulsion ofwater and hydrocarbons.

The petroleum industry has long sought economical and efficient methodsfor breaking mixtures produced from surfactant-based floods, inparticular their microemulsion component, and for recovering valuablechemicals contained in such mixtures for reuse in cEOR.

For example, GB 2 146 040 describes a method for breakingoil-water-surfactant emulsions that have as one component amicroemulsion. This method separates oil, brine, and surfactant, toproduce pipeline quality oil and an injectable brine/surfactant phase bycarefully controlling temperature and salinity within certain operableranges.

US2009/0281003 relates to a method in which chemicals in a cEOR streamare forced into either an aqueous or an organic phase and are thenconcentrated and re-injected into an oil-bearing formation.

However, there remains a need for sustainable and cost-effective andmethods and systems for separating hydrocarbons from cEOR mixtures.Accordingly, the present invention seeks to solve the technical problemof providing a more sustainable and/or cost-effective hydrocarbonseparation method and system than the prior art.

SUMMARY OF INVENTION

From a first aspect, the invention resides broadly in a method ofseparating a hydrocarbon phase from an input mixture comprising anemulsion of water and hydrocarbons in the presence of a surfactant(surface-active agent), the method comprising: adjusting the salinity ofthe mixture to release hydrocarbons and water from the emulsion into ahydrocarbon phase and a salt-containing aqueous phase respectively; andseparating at least a part of the hydrocarbon phase from thesalt-containing aqueous phase, wherein at least a part of thesalt-containing aqueous phase is recovered (or retained) for furtheruse.

As the input mixture comprises hydrocarbons, water, and a surfactant, ittypically comprises, at least as one component, a microemulsion. Theinterfacial tension between hydrocarbons and water in the input mixturemay for example be below 1 dyne/cm.

The input mixture may preferably be a mixture produced by cEOR and maytherefore further include a co-surfactant, a co-solvent or otherchemicals, as is known in the art. Additionally, cEOR mixtures have asalinity consistent with operational requirements for hydrocarbonsrecovery. As lowering interfacial tension is a key objective, some cEORmixtures may be at or close to “optimal salinity”. Thus the inputmixture may advantageously have a salinity at or close to its “optimalsalinity”. However, the salinity of the input mixture may vary, e.g.based on operational requirements for hydrocarbons recovery, or as aresult of treatment, dilution or concentration carried out before themethod of the invention.

Salinity is known to have an impact on interfacial tension inwater-hydrocarbons-surfactant mixtures, and is therefore a statevariable that is used in the present invention to control, particularlyreduce, the degree of emulsification in such mixtures, with the aim ofseparating a hydrocarbon phase. Other state variables, such astemperature and pressure, may advantageously be kept substantiallyconstant.

The method of the invention enables particularly effective andsustainable use of salinity as a state variable in the separation ofhydrocarbons from emulsions, especially microemulsions, such as thoseobtained from cEOR. Specifically, by including the recovery of at leasta part of the salt-containing aqueous phase, the method of the inventionenables reuse of salt and/or water to adjust the salinity of the inputmixture. Thus, in the method of the invention, salt and/or water neednot be sacrificed during the hydrocarbon separation process. This is asignificant advantage in the context of large-scale operations, wherethe costs of obtaining water, and especially salt, as well as associatedtransportation costs, may be significant commercial factors.

Accordingly, in a preferred embodiment of the invention, the method maycomprise reusing at least a part of the salt-containing aqueous phase,for example salt and/or water contained therein, to adjust the salinityof the mixture as described above.

To provide maximum opportunity to reuse the salt-containing aqueousphase, the method of the invention may be operated continuously, in thesense that more than one batch of input mixture may be subjected(successively) to the method of the invention. Most advantageously, themethod may be carried out in a continuous flow.

Alternatively the method may be carried out in a plurality of batches.Batch operation of the method is typically less effective thancontinuous flow operation but may be of particular benefit where themethod is to be used intermittently, or where individual steps of themethod are to be carried out in geographically distinct locations, as isoptionally contemplated within the scope of the invention.

The release of hydrocarbons and water from an emulsion into ahydrocarbon phase and a salt-containing aqueous phase may beaccomplished by either an increase or a decrease in salinity. Thusadjusting the salinity of the input mixture may comprise eitherincreasing or decreasing the salinity of the mixture. An increase insalinity may be achieved by adding salt to the input mixture and/or byremoving water from the input mixture, whereas a decrease in salinitymay be achieved by removing salt from the input mixture and/or addingwater to the input mixture.

The choice between increasing and decreasing the salinity of the inputmixture is particularly apparent in the context of input mixtures, forexample derived from cEOR, that are at or close to “optimal salinity”.In such mixtures, a relatively small adjustment of salinity, be it anincrease or a decrease, can result in the release of hydrocarbons andwater from the emulsion in the input mixture, i.e. the breaking of theemulsion.

In mixtures having a salinity above “optimal salinity”, an increase insalinity may be more economical, whilst in mixtures having a salinitybelow “optimal salinity” a decrease may be more economical. However,operational considerations play a dominant role in choosing whether toadjust the salinity of the input mixture by increasing or decreasingsalinity. It is hence preferred in the present invention to adjust thesalinity of the input mixture by increasing the salinity of the inputmixture, as this provides particular opportunities for the reuse of therecovered salt-containing aqueous phase, as will be explained.

To enable particularly effective reuse of the salt-containing aqueousphase, the method may further comprise desalinating the salt-containingaqueous phase to provide a first stream having a relatively highsalinity and a second stream having a relatively low salinity.Desalination may be carried out in any suitable desalination station orunit, for example by nanofiltration and/or reverse osmosis.

The first, high salinity stream may advantageously be used (or recycled)to increase the salinity of the mixture, i.e. to aid emulsion breakingas described above. To fulfil this function, the high salinity streammust have a salinity which is higher than the salinity of the inputmixture. Thus the high salinity stream may advantageously have asalinity above the salinity of the input mixture.

The surfactant in the input mixture is generally distributed in both thewater and the hydrocarbons. Following salinity adjustment of themixture, there occurs a shift of surfactant (and any co-solvent that maybe present) into either the hydrocarbon phase (if the salinity isincreased) or the aqueous phase (if the salinity is decreased). However,this shift is not complete and therefore there always remains at leastsome surfactant (and co-solvent if present) in the hydrocarbon phaseseparated from the mixture, often along with a significant concentrationof salt. This concentration of surfactant may be undesirable for furtherprocessing or use of the hydrocarbon phase, particularly where asalinity increase of the input mixture has driven substantial amounts ofsurfactant into the hydrocarbon phase. Also, surfactant that remains inthe hydrocarbon phase is lost for the purpose of cEOR and thereforerepresents an additional cost of the cEOR process. To mitigate the lossof surfactant and purify the hydrocarbon phase, the method of theinvention may advantageously further comprise washing the hydrocarbonphase to recover surfactant and optionally salt therefrom.

Conveniently, the low salinity stream produced by desalination of thesalt-containing aqueous phase may be reused to wash the hydrocarbonphase to recover surfactant and optionally salt therefrom. As it isundesirable for the hydrocarbon phase to form a stable emulsion with thelow salinity stream, the low salinity stream may preferably bedesalinated such that its salinity is lower than the salinity of theinput mixture. Thus, to cater for typical cEOR input mixtures, the lowsalinity stream may have a salinity below “optimal salinity”.

After washing, the hydrocarbon phase may preferably be separated to forma purified crude oil stream, leaving behind an aqueous surfactantrecovery stream. The surfactant recovery stream may advantageously bere-injected into a hydrocarbons bearing formation in a cEOR process,optionally in combination with salt from the first, high salinitystream.

From a second aspect, the invention broadly resides in a hydrocarbonsseparation system suitable for performing the method according to thefirst aspect of the invention, the system comprising: an inlet forintroducing a mixture comprising an emulsion of water and hydrocarbonsin the presence of a surfactant; a salinity adjustment station foradjusting the salinity of the mixture; separating means for separatingfrom the mixture a hydrocarbon phase and a salt-containing aqueousphase; and recovery means for recovering at least a part of thesalt-containing aqueous phase for further use.

The recovery means may advantageously comprise a conduit for recyclingat least a part of the salt-containing aqueous phase to the salinityadjustment station to adjust the salinity of the mixture.

To aid separation of the hydrocarbon phase from the aqueous phase, theseparation system may comprise a membrane, for example of the ceramictype. The membrane may act as the sole separating means or may becombined with a phase separation vessel.

For effective further use of the salt-containing aqueous phase, thesystem may further comprise desalination means for desalinating thesalt-containing aqueous phase to provide a first stream with arelatively high salinity and a second stream with a relatively lowsalinity. The desalination means may comprise a reverse osmosis unit, ora nanofiltration unit, or a nanofiltration, ultrafiltration ormicrofiltration unit upstream of a reverse osmosis unit.

Preferably, the system may comprise a conduit for channelling the firststream to the salinity adjustment station to increase the salinity ofthe mixture.

The system may advantageously further comprise washing means for washingthe hydrocarbon phase and recovering a surfactant recycle stream, and aconduit for channelling the second, low salinity stream to the washingmeans. The additional advantage of a surfactant recycle in the system,is that it becomes a self-sufficient system.

The invention contemplates the further use and reuse of variouscomponents separated from a mixture comprising water, hydrocarbons and asurfactant. Thus, from a third aspect, the invention resides in achemical enhanced oil recovery process comprising injecting surfactantrecovered from a hydrocarbon phase as described anywhere herein into ahydrocarbon-bearing formation. Preferably, the surfactant may becombined with salt recovered as described anywhere herein, for exampleprior to injection.

Unless otherwise indicated, terms used herein are to be construed basedon their standard definition in the art. Similarly, unless otherwiseindicated, parameters provided herein are based on the relevant standardmeasuring techniques (ISO where available).

The term “emulsion” as used herein refers simply to a mixture of two ormore immiscible liquids.

Those skilled in the art will appreciate that an emulsion of water andhydrocarbons in the presence of a surfactant can lead to the formationof at least an amount of a “microemulsion”, i.e. a thermodynamicallystable emulsion.

The term “interfacial tension” as used herein refers to the strength ofthe film separating two immiscible fluids (hydrocarbons and water)measured in dynes per centimetre, according to ASTM D971.

The term “salt” as used herein refers to all salts soluble in water.Sodium chloride is a preferred salt.

The term “salinity” as used herein refers to the amount of dissolvedsalt in water. Salinity referred to herein may be determined accordingto the Practical Salinity Scale 1978 (PSS78), originally developed forseawater, which involves a conductivity comparison to a solution of32.4356 g/kg KCl at 15° C.

The term “optimal salinity” as used herein refers to the saltconcentration that produces the lowest interfacial tension between oiland hydrocarbons in a given mixture of hydrocarbons, water and asurfactant. It may be measured by standard interfacial tensionmeasurements or be derived from other methods like phase behaviour teststhat are known to persons skilled in the art.

The term “surfactant” or “surface active agent” as used herein refers toany chemical agent capable of reducing the interfacial tension betweenhydrocarbons and water.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will now be described, by way of example only, withreference to the accompanying drawings in which:

FIG. 1 is a schematic diagram of a hydrocarbons separation system forseparating hydrocarbons from a hydrocarbons recovery mixture accordingto a first embodiment of the invention;

FIG. 2 is a schematic diagram of a hydrocarbons separation system forseparating hydrocarbons from a hydrocarbons recovery mixture accordingto a second embodiment of the invention; and

FIG. 3 is a schematic diagram of a hydrocarbons separation system forseparating hydrocarbons from a hydrocarbons recovery mixture accordingto a third embodiment of the invention.

With reference to FIGS. 1 to 3, the hydrocarbons separation systems andmethods (or processes) according to three exemplary embodiments of theinvention described below each serve to extract or separate ahydrocarbon phase from an input mixture. The input mixture comprises anemulsion of water and hydrocarbons in the presence of a surfactant(surface-active agent). Whilst the input mixture could stem from anysuitable source, in practice, such mixtures are most commonly obtainedfrom chemical enhanced oil recovery (cEOR) streams.

The hydrocarbons separation systems and methods according to the threeexemplary embodiments of the invention comprise adjusting, specificallyincreasing, the salinity of the input mixture to release hydrocarbonsand water from the emulsion into a hydrocarbon phase and asalt-containing aqueous phase respectively. Thereafter, at least a partof the hydrocarbon phase is separated for further use, and at least apart of the salt-containing aqueous phase is recovered for reuse.

To maximise efficiency, the methods according to the exemplaryembodiments of the invention are each carried out in a continuous flowmanner, in a single system or facility. However, it will be appreciatedthat the individual stages of the methods could also be performed inbatches, either in a single facility, or in several geographicallydistinct locations.

Referring firstly to FIG. 1, in a first embodiment of the invention, aconventional emulsified cEOR mixture 1 comprising hydrocarbons (in theform of crude oil), water and a surfactant is input into a hydrocarbonsrecovery system.

The surfactant in the cEOR mixture 1 may be of any known type suitablefor cEOR. In addition to surfactants, the cEOR mixture may compriseother additives as known in the art.

The cEOR mixture 1 has an original salinity that supports effectivecEOR, at which the surfactant provides a lowered interfacial tensionbetween the oil and the water, e.g. in the order of less than 1 dyne/cm.Usually, the cEOR mixture 1 is at or close to optimum salinity.

To reduce the degree of emulsion in the cEOR mixture 1, i.e. to releaseoil and water into separate oil and aqueous phases, the mixture isinitially channelled to a salinity adjustment station S. Salinity has astrong impact on the ability of surfactants to lower surface tension incEOR mixtures. For example, high salinities, in excess of the “optimumsalinity” of a cEOR mixture, cause microemulsions to be broken, leadingto the formation of increased oil (or hydrocarbons) and aqueous (orwater) phases. The salt content of the mixture tends to dissolve mainlyin the aqueous phase, although some salt will also be present in the oilphase, whilst an increased proportion of surfactant is pushed into thehydrocarbons oil with increasing salinity.

In the salinity adjustment station S, which may for example simplycomprise a suitable conduit (as in FIGS. 1-3) or vessel, a high-salinityinput 11 is mixed with the cEOR mixture 1 to increase the salinity ofthe mixture to a salinity in excess of the “optimum salinity” of thecEOR mixture. The high-salinity input 11 has a greater salinity than thecEOR mixture 1 and comprises recycled salt, as will be described later.

The ratio at which the cEOR mixture 1 and the high-salinity input 11 aremixed depends on a number of factors, such as the composition (includingsalinity) of the cEOR mixture 1 and the salinity of the high salinityinput 11. The skilled person may choose to determine the requisitesalinity increase in the mixture 2 simply by carrying out periodicvisual inspections to determine whether the degree of emulsion in thecEOR mixture 2 is reduced.

The salinity-increased EOR mixture 2, with its increased oil and aqueousphases, is channelled into a phase separation (or demulsifier) vessel A.Phase separation vessels are well known in the art and make use ofdifferences in density to separate oil and aqueous phases. The phaseseparation vessel A, and indeed all phase separation vessels mentionedherein, may take any suitable form and may for example be of the typedescribed in Perry's Chemical Engineer's Handbook, 6^(th) edition, page21-64 and further.

The phase separation vessel A separates the salinity-increased EORmixture 2 into an oil phase 3 and an aqueous phase 6. The oil phase 3 ispurified to provide crude oil, as will be described, whilst the aqueousphase 6 is recovered for further use, specifically for reuse in salinityadjustment.

Referring still to FIG. 1, the aqueous phase 6 is channelled via amembrane M to a desalination station B. The membrane M serves to removeany remaining oil from the aqueous phase 6. As the skilled reader isaware, the process of phase separation typically only provides a certaindegree of purity, which in the case of the aqueous phase 6 issupplemented by the use of the membrane M. The membrane M may be anymembrane suitable for removing hydrocarbons from water, such as forexample a ceramic membrane. Suitable ceramic membranes comprise TiO₂,ZrO₂, Al₂O₃ or SiC. The pore size of a suitable ceramic membrane issuitably smaller than 100 nm, preferably smaller than 50 nm, morepreferably smaller than 30 nm and most preferably smaller than 10 nm. Ahydrophobic membrane may be used, the use of which results in anefficient removal of the oil phase from the water phase. Suitablehydrophobic membranes include grafted ceramic membranes, for example agrafted ZrO₂-containing membrane, and polymeric membranes, for examplepoly(dimethylsiloxane) (PDMS) or poly-imide based membranes.

Following deep oil removal by the membrane M, the aqueous phase 6 entersthe desalination station B, where it is processed into a low salinitystream 7 and a high salinity stream 8. The desalination station B mayemploy conventional reverse osmosis or nanofiltration technology, suchas that disclosed in “Reverse Osmosis—A Practical Guide for IndustrialUsers”, W. Byrne, Tall Oaks Publishing Inc., March 1995.

The high salinity stream 8 produced by the desalination station B may beused wholly or partly as the high salinity input 11 added to the cEORmixture in the salinity adjustment station S. Where only partial use ofthe high salinity stream is desired in the salinity adjustment stationS, for example to prevent an excessive build-up of salinity in thesystem, the high salinity stream 8 may be split at a salinity outlet 10.The salinity outlet 10 may remove salt from the system, for example foruse in cEOR reinjection 12.

The aqueous low salinity stream 7 produced by the desalination station Bis used to wash the oil phase 3 resulting from phase separation of thecEOR mixture 2. Referring still to FIG. 1, the oil phase 3 typicallycontains a substantial concentration of surfactant as a result of thesalinity increase in the cEOR mixture, together with some salt.Therefore, the low salinity stream 7, is mixed with the oil phase 3 toform a mixture with a salinity below “optimum salinity” in whichsurfactant and salt are washed out of the oil by the low salinitystream. Despite the presence of surfactant, the mixture shows onlyminimal emulsification because of the low level of salinity.Furthermore, surfactant and salt are washed from the oil phase 3 intothe low salinity stream 7, turning the low salinity stream into anaqueous surfactant recycle stream 9 and the oil phase into a washedcrude oil stream 5.

The surfactant recycle stream 9 is separated from the crude oil stream 5in a second phase separation (demulsifer) vessel C. The crude oil stream5 may be refined and processed further as desired, whilst the surfactantrecycle stream 9, containing substantial concentrations of surfactantand salt may be used for cEOR reinjection 12.

Notably, the crude oil stream 5 is particularly suitable for furtherrefining because it has already been desalinated, saving on desalinationoperations at the refinery.

In summary, the hydrocarbons separation system and method according tothe first exemplary embodiment of the invention envisage increasing thesalinity of a cEOR mixture to break emulsions (particularlymicroemulsions) therein, separating a hydrocarbon phase from the cEORmixture for further use, reusing or recycling salt from the remainingaqueous phase within the separation system, and reusing water andoptionally remaining salt from the aqueous phase for cEOR reinjection.

Referring now to FIG. 2, a hydrocarbons separation system and methodaccording to a second embodiment of the invention is identical to thesystem and method according to the first embodiment of the invention,with like reference numerals being used for like parts, save for theworking of the desalination step in station B.

The desalination station of the system according to the secondembodiment of the invention comprises a nanofiltration unit B1 arrangedin series with a reverse osmosis unit B2. Alternatively, nanofiltrationunit B1 may be an ultrafiltration unit or microfiltration unit (notshown in FIG. 2). The advantage of this arrangement is that it enablesthe removal of divalent cations from the system. Specifically, thenanofiltration unit B1 removes and discards divalent cations.Thereafter, the reverse osmosis unit B2 processes the remaining salt andwater in the salt-containing aqueous phase 6 in the manner of thedesalination station B of the first embodiment of the invention, to formthe high salinity stream 8 and the low salinity stream 7.

Referring now to FIG. 3, a hydrocarbons separation system and methodaccording to a third embodiment of the invention is identical to thesystem and method according to the first embodiment of the invention,with like reference numerals being used for like parts, save that themembrane M acts as a phase separator, thereby eliminating the need for adistinct phase separation vessel.

Phase separation in the third embodiment of the invention occurs at themembrane M, which permits only the passage of aqueous phase, but not ofthe hydrocarbon phase. The passage of aqueous phase through the membraneM, as well as the addition of salt by the high salinity input 11, causean increase in salinity and consequential breaking of the emulsionwithin the input mixture 2, i.e. the release of hydrocarbons and waterfrom emulsion into the hydrocarbon phase and aqueous phase respectively.The hydrocarbon phase can then be channelled and separated for furtherprocessing using gravimetric principles and techniques known in the art,whilst the aqueous phase continues, via the membrane M, to desalinationstation B.

Notably, the use of membrane M as a phase separator enables an increasein the salinity of the input mixture by the removal of water rather thanthe addition of salt. Accordingly, in a variant of the third embodimentof the invention, input of salt at the salinity adjustment station S isnot necessary and hence omitted, meaning that salt in the high salinitystream 8 may be reused elsewhere for example in cEOR reinjection 12, viasalt outlet 10.

It will be appreciated that certain aspects of the method according tothe first, second and third embodiments of the invention arenon-essential and may be omitted, modified or replaced without departingfrom the scope of the invention. Notably, it is within the scope of theinvention to modify the embodiments so that water instead of salt isrecycled to the salinity adjustment station, in which case the salinityof the input mixture is decreased to break the emulsion, rather thanincreased.

1. A method of separating a hydrocarbon phase from a mixture comprisingan emulsion of water and hydrocarbons in the presence of a surfactant,the method comprising: adjusting the salinity of the mixture to releasehydrocarbons and water from the emulsion into a hydrocarbon phase and asalt-containing aqueous phase respectively; and separating at least apart of the hydrocarbon phase from the salt-containing aqueous phase,wherein at least a part of the salt-containing aqueous phase isrecovered for further use.
 2. A method according to claim 1, furthercomprising reusing at least a part of the salt-containing aqueous phaseto adjust the salinity of the mixture.
 3. A method according to claim 1,wherein the salinity of the mixture is adjusted by increasing thesalinity of the mixture.
 4. A method according to claim 1 furthercomprising desalinating the salt-containing aqueous phase to provide afirst stream having a relatively high salinity and a second streamhaving a relatively low salinity.
 5. A method according to claim 4further comprising reusing the high salinity stream to increase thesalinity of the mixture.
 6. A method according to claim 4 furthercomprising reusing the low salinity stream to wash the hydrocarbon phaseto recover surfactant.
 7. A hydrocarbons separation system comprising:an inlet for introducing a mixture comprising an emulsion of water andhydrocarbons in the presence of a surfactant; a salinity adjustmentstation for adjusting the salinity of the mixture; separating means forseparating from the mixture a hydrocarbon phase and a salt-containingaqueous phase; and recovery means for recovering at least a part of thesalt-containing aqueous phase for further use.
 8. A system according toclaim 7 wherein the recovery means comprises a conduit for recycling atleast a part of the salt-containing aqueous phase to the salinityadjustment station to adjust the salinity of the mixture.
 9. A systemaccording to claim 7 comprising a membrane for separating thehydrocarbon phase from the aqueous phase.
 10. A system according toclaim 9, wherein the membrane acts as the separating means, either aloneor in combination with a phase separation vessel.
 11. A system accordingto any one of claim 7, further comprising desalination means fordesalinating the salt-containing aqueous phase to provide a first streamwith a relatively high salinity and a second stream with a relativelylow salinity.
 12. A system according to claim 11, wherein thedesalination means comprises a reverse osmosis unit, a nanofiltrationunit, or a nanofiltration unit upstream of a reverse osmosis unit.
 13. Asystem according to claim 11 further comprising washing means forwashing the hydrocarbon phase and recovering a surfactant recyclestream, and a conduit for channelling the second, low salinity stream tothe washing means.
 14. A chemical enhanced oil recovery processcomprising injecting surfactant recovered by the method of claim 5 intoa hydrocarbon-bearing formation.
 15. A chemical oil recovery processaccording to claim 14 wherein the surfactant is combined with salt fromthe high salinity stream.